In many parts of the country, summer means mosquitoes. And in a lot of places mosquitoes are controlled with pesticides. But in South Florida, conservationists are worried that pesticides could do harm to other animals, especially butterflies. Here's NPR's Greg Allen.

GREG ALLEN, BYLINE: There are few places where mosquito control is as important as Florida. In the 19th century, the yellow fever epidemic prompted the state to begin mosquito control efforts that today are carried on by the counties. In Miami, the man in charge is Chalmers Vasquez. At the operations center, he opens the tailgate on a pickup truck...

(SOUNDBITE OF TAILGATE OPENING)

ALLEN: ...And shows off his main tool for controlling mosquitoes.

CHALMERS VASQUEZ: This is what is called aerosol generator - mosquito spray.

ALLEN: Most days in the early morning hours, Vasquez sends trucks out to neighborhoods where mosquitoes are a problem. He has 10 trucks equipped with aerosol sprayers, but rarely uses all at once.

VASQUEZ: When we need to use a lot of trucks, that means we need to airplane because the area is so big we cannot manage spraying and killing the mosquito with just with a - by truck.

ALLEN: Airplane means conducting aerial spraying.

(SOUNDBITE OF AIRPLANE FLYING OVER)

ALLEN: In Miami, it's a job often done by an Air Force Reserve unit flying C-130 aircraft like this one. There are some though in South Miami who question the wisdom of blanket spraying pesticides that affect not just mosquitoes but also many other animals. Philip Stoddard is a professor of biological science at Florida International University. He lists some of the other species affected by mosquito spraying.

PHILIP STODDARD: The natural predators like dragonflies and spiders, which are pretty effective on mosquitoes - and they've been wiped out and they don't recover so quickly. The native songbirds, which depend on little caterpillars to survive, feed their young, carry out successful migrations, they've been knocked back.

ALLEN: Along with being a biology professor, Stoddard is also the mayor of South Miami. The city commission there recently voted to designate the town as a wildlife sanctuary. They told the county to stop spraying in the town limits except when it's needed to combat mosquito-borne diseases, like dengue fever or chikungunya. The county concedes that spraying mostly combats salt marsh mosquitoes, which are a nuisance but don't carry disease. The mosquitoes which do spread disease, Stoddard notes, breed and stay in neighborhoods wherever there's standing water.

STODDARD: And the only way we're going to be able to combat these diseases effectively and keep them out of our suburban neighborhoods is by going back to the old methods of getting the darn standing water out of here.

ALLEN: Mosquito control manager Chalmers Vasquez says Florida law requires his department to respond when residents complain about mosquitoes. Despite requests from South Miami to make it a spray-free zone, at this point, he says, the county has no plans to do so.

VASQUEZ: You know, we've been applying pesticide area - in that area since the mid-'60s. And insect fauna is still there.

ALLEN: Studies show, however, the chemicals used to kill mosquitoes also take a toll on other insects. Butterflies are especially susceptible. Emphasizing that point, the U.S. Fish and Wildlife Service recently put on its endangered species list two butterflies found only in South Florida. The Bartram’s Hairstreak and the Florida leaf wing butterflies have declined precipitously, mostly because of habitat loss. But Mark Salvato, a biologist with the agency, says pesticides are also a factor. Salvato says mosquito control authorities try to minimize the impact by avoiding protected areas and spraying at times when butterflies aren't active.

MARK SALVATO: There's a general rule - the spray goes into the vegetation. It goes through the air. It's pretty indiscriminate and what it hits despite everyone's best intentions.

ALLEN: In South Miami, town officials are hoping to build support for mosquito control strategy that safeguards public health without devastating butterflies and other sensitive species. Greg Allen, NPR News, Miami. Transcript provided by NPR, Copyright NPR.